An Advanced Well Log and an Effective Methodology to Evaluate Water Saturation of the Organic-Rich Cambay Shale
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Original Paper
An Advanced Well Log and an Effective Methodology to Evaluate Water Saturation of the Organic-Rich Cambay Shale Sanjukta De
1,2
and Debashish Sengupta1 Received 16 June 2020; accepted 1 October 2020
Water saturation (Sw) is a vital parameter in the evaluation of hydrocarbon reservoir. Realistic estimation of Sw in shale reservoir is a challenging problem because of the presence of significant clay minerals and organic matter. The present study aims to estimate Sw of organic-rich Cambay Shale, Jambusar–Broach block, Cambay Basin, India, using an effective methodology and improved equation (TOC–clay equation), considering the appropriate corrections to counter the effect of clay minerals and organic matter in modifying resistivity. Advanced log like Litho-scanner has been utilized for the continuous estimation of clay content and total organic carbon (TOC), required for the estimation of Sw. Elemental capture spectroscopy and support vector regression were also applied for evaluation of clay content and TOC in one well where Litho-scanner log is not available. To investigate the effectiveness and applicability of the TOC–clay equation, results of Sw estimated from this equation and various other models have been compared with core Sw for a well. The analysis indicates that Sw derived from TOC–clay equation is having the closest agreement to core Sw data with an average absolute percentage error of 7.9% and coefficient of correlation 0.95. For other models, average absolute errors are significantly higher (16.8–32.7%). The application of TOC–clay equation will be useful for evaluation of the Cambay Shale reservoir. In addition, the resistivity-based TOC–clay equation used in this study is simple with a practical approach; it can be applied easily and efficiently for any organic-rich shale reservoir elsewhere. KEY WORDS: Cambay Shale, Water saturation, TOC–clay effect, Litho-scanner log, ArchieÕs equation.
INTRODUCTION Estimation of hydrocarbon reserve for any reservoir is a primary requirement for economic evaluation prior to draw a field development plan for extraction of hydrocarbon. Hydrocarbon saturation (Sh) of a reservoir is determined from water 1
Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India. 2 To whom correspondence should be addressed; e-mail: [email protected]
saturation (Sw) as one minus Sw. Water saturation and porosity are two key parameters in the evaluation of hydrocarbon reserve (Gupta et al. 2012; Kadkhodaie and Rezaee 2016; Liu et al. 2018). These parameters are very sensitive and inaccurate estimation of these parameters will lead to either underestimation or overestimation of reserve and thus will affect economic evaluation for taking decision. For unconventional shale reservoir, accurate estimation of these parameters is very difficult particularly water saturation (Kadkhodaie and Re-
Ó 2020 International Association for Mathematical Geosciences
De and Sengupta zaee 2016; Zhang and Xu 2016). Fortunately,
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